This invention concerns equipment and methods for circulating liquids generated in industrial processing, such as the cutting fluids used in machine tools during the machining of parts.
In the large scale production of machined parts, such as automotive engine parts, it is a common practice to arrange a series of machine tools along a transfer line, with parts transferred down the line for step by step completion of the necessary machining operations on the parts. Cutting fluid is directed at the tools doing the cutting of metal for cooling, lubrication, and to carry off the chips and other debris generated by the machining of the part. The cutting fluid drains down from each machine tool, carrying the chips and other debris with it into a collection trench. The collected cutting fluid liquid moves down the trench carrying the chips, etc. to a sump, from which the mixture is pumped and directed to filtration equipment for removal of the contaminants, and then recirculated to the machine tools for reuse
In the past, below grade trenches were commonly used, with sloping trench bottoms causing gravity flow of the collected liquid and entrained chips down the length of the trench, the flow sometimes assisted with pumped jets of liquid.
In recent years, below grade trenches have become disfavored due to the cost of excavating and lining the trenches with metal plates, as well as the difficulties encountered when a reconfiguration of a plant floor plan becomes necessary, and also because of the potential for hard-to-detect leaks occurring, possibly contaminating the soil beneath the plant.
Above grade troughs have thus been recently adopted, as for example, as shown in U.S. Pat. No. 5,980,735, issued to the present inventor.
The manufacturers wish to avoid raising the machine tools above normal working heights so that plant personnel do not have to climb onto raised platforms to replace tools or perform maintenance.
These constraints impose certain limitations on the collection trough system as there is only limited above grade vertical space available beneath the machines, and typically liquid drains from a number of machines into a common trough. A sufficient flow rate must be maintained to carry the chips and other debris down the trough, and this also limits the height of the trough bottom and the depth of liquid at the downstream end as there must be adequate slope to achieve the flow velocity required to carry off the chips. The result is a quite shallow depth stream of liquid flow at the downstream end of the trough.
It is difficult to reliably pump out liquid and chips from a shallow stream of liquid, as pumps will lose prime as the depth of flow at the trough end and rises and falls. It is critical that the flow be constant, as even momentary back ups will cause the chips carried by the flow stream to pile up, and if too many chips pile up, these will not be carried away when the flow resumes.
Such machine tool systems operate continuously for many hours or days at a time while producing a sporadic volume of collected liquid, and as it is impractical for most pumps to run dry, starting and stopping the pumps would be necessary, aggravating any tendency for a pump to lose prime.
One possible approach to this problem is to draw out the liquid and chips with a vacuum suction created by a draw tube connected to a vacuum tank, as described in applicant""s prior U.S. Pat. Nos. 5,593,596 and 5,466,380, which also shows providing individual sumps at each machine tool.
This approach is effective for moderate flow volume systems, but for high volume installations, i.e., those generating volumes on the order of 1000 g.p.m., the piping and tank sizes become impractically large. Furthermore, there are difficulties in maintaining a sufficient vacuum in a large tank where air may periodically be vented into the tank without sometimes developing vacuums too low to maintain evacuation of the sumps.
Another approach would be to provide a below grade gravity collection sump at the downstream end of the trough, but as noted, below grade pits are undesirable, and chips and other solids tend to settle out in such pits, requiring periodic maintenance.
It is the object of the present invention to provide a lift station and method which is capable of very reliably handling such shallow depth varying volume liquid flow streams carrying debris, without the occurrence of even momentary stoppages of the flow stream.
The above object as well as others which will become apparent upon a reading of the following specification and claims, are achieved by arranging a lift station comprised of a bladed wheel in a housing at the downstream end of the collection trough. The housing is connected to the trough end so as to receive the flow stream into an inlet opening, and passes it into a slightly downwardly inclined surface defined by the inside of a housing bottom wall. The bladed wheel is oriented so that its outwardly extending blades are shaped in conformity to the housing section, and sweep down the inclined surface in the same direction as that of the flow stream, tending to sweep the incoming liquid and debris down the inclined surface. The housing bottom wall blends into to a curving perimeter wall at the rear of the housing which extends upwardly and towards a reversely inclined exit chute. The bladed wheel is rotated with sufficient speed such that the liquid swept along with the blades is slung out from the blades and into the exit chute with sufficient velocity so that the liquid has enough momentum to reach and pass over a weir edge at the upper end of the exit chute. The blades are preferably raked back tangentially to insure that the liquid is not captured by the blades and is readily slung out as the blades rotate over the top of the wheel hub.
Any liquid which does not reach the weir edge flows back downwardly onto a surface defined by a housing front wall which has a forwardly extending bottom lip which redirects the liquid flow in the same direction as that of the incoming flow stream to again be directed upwardly as the wheel blades carry the liquid around again. This additional momentum in a forward direction insures that a velocity of the redirected liquid will be achieved sufficient to reach the weir edge.
The liquid flowing over the weir edge flows into an outlet chute and thence into a collection tank, able to be filled to a level such that it can easily be pumped to a filtration apparatus. A chip shredder/conveyor can be mounted in the outlet chute to reduce the chip size for easier subsequent handling.
As noted, the blades are preferably mounted to extend tangentially back from the direction of rotation to improve lifting performance, but this also will allow deflection if solid objects are dropped into the liquid flow and reach the bladed wheel, and these objects thus can be accommodated without breakage of the blades or stoppage of the wheel.
Several of the bladed wheel and housing devices can be used to lift liquid flows through successive inclined trough sections extending over the same level.